A size of a transmitting/receiving module for use in infrared data communication has been reduced. Further, performance of such a transmitting/receiving module has been improved, and its processing speed has been accelerated. In regard to the acceleration of the processing speed, it is necessary that the transmitting/receiving module be capable of handling a conventional low-speed communication as well as a high-speed communication, so that the transmitting/receiving module is compatible, in terms of communication, with a conventional low-speed devices. In short, it is necessary that the transmitting/receiving module support the low-speed communications as well as the high-speed communications. The most important problem to be solved for achieving this is performance of a receiving device. In the receiving device, a pulse needs to be reproduced based on a communication speed, and this pulse is transmitted to a controller LSI in a latter stage. This receiving device needs to support various communication speeds.
An example of the prior art is disclosed in Japanese Unexamined Patent Application No. 2000-115078 (Tokukai 2000-115078; published on Apr. 21, 2000).
FIG. 9 is a block diagram illustrating a conventional receiving system for use in a infrared data communication. In a typical arrangement of a receiving circuit 101 for use in an optical communication, a photocurrent signal (optical signal pulse) is inputted via a photodiode chip (PD), and is amplified in amplifying circuits 21 and 22 in an integrated receiving chip. Then, in a hysteresis comparator 23, a pulse-reshaping process is carried out with respect to the amplified photocurrent signal by comparing the amplified photocurrent signal with a threshold “Thresh” for use in measuring a signal, so as to convert the amplified photocurrent signal into a digital signal (received pulse). Then, the digital signal is outputted in the form of pulse to a received output (VO). The received output (VO) is connected to the controller LSI (not shown), and the digital signal outputted from the received output is processed in the control LSI. In order to accelerate the communication speed, frequency bands of the amplifying circuits 21 and 22 are increased so as to correspond to the high speed communication. Alternatively, performance of the pulse generating circuit (hysteresis comparator circuit 23) is improved. However, for example, the following problems occur when increasing the frequency bands or accelerating the performance of the pulse generating circuit. Namely, an internal noise level is increased in the receiving device on account of an increase in the frequency bands. Further, an increase of unwanted noise or the like problem takes place on account of an acceleration in the processing speed of the pulse generating circuit.
In view of the foregoing problems of noise, a common infrared data communication standard known as IrDA defines standards of reception sensitivity which are different from one another on a transmission speed basis. In a low-speed communication of 2.4 kbps to 115.2 kbps, the sensitivity of the receiving device is defined as 4 μW/cm2. In a high-speed communication of over 115.2 kbps (e.g. 576 kbps, 1.152 Mbps, 4 Mbps, and 16 Mbps), the sensitivity is defined as 10 μW/cm2. That is, the sensitivity is so defined that the sensitivity in the high-speed communication is 2.5 times of the sensitivity in the low-speed communication.
Conventionally, the receiving device has been so arranged that properties of the receiving circuit are switched over depending on the communication speeds. In the case of FIG. 9, a terminal (MODE) is the terminal for switching the properties.
However, due to the trend of reducing a size of an apparatus having an infrared transmitting/receiving module device, a size of the device needs to be even smaller, and the number of terminals in the device needs to be reduced. This calls for a measure which eliminates a need of switching-over terminals.